Decision Height (DH) is a critical concept in aviation that directly affects flight safety during instrument approaches. Used primarily in precision approaches, decision height determines the exact point at which a pilot must decide whether to continue the landing or execute a missed approach.
Decision Height
What Is Decision Height (DH)?
Decision Height (DH) is the specified height above the runway elevation at which a pilot must decide to either:
Continue the approach and land, if required visual references are acquired, or
Initiate a missed approach, if visual cues are insufficient.
Decision height is measured above runway threshold elevation, not above mean sea level.
Decision Height Definition (ICAO)
According to ICAO (International Civil Aviation Organization):
Decision Height is the height above the runway threshold elevation at which a missed approach must be initiated if the required visual reference has not been established.
This definition is universally accepted and applied in instrument flight rules (IFR) operations.
Where Decision Height Is Used
Decision height is used in precision instrument approaches, including:
ILS (Instrument Landing System) CAT I
ILS CAT II and CAT III (with variations)
GLS (GBAS Landing System)
PAR (Precision Approach Radar)
Non-precision approaches use Decision Altitude (DA) instead of DH.
Lower decision heights require advanced aircraft systems, crew training, and ground equipment.
Importance of Decision Height in Aviation Safety
Decision height plays a vital role in:
Preventing controlled flight into terrain (CFIT)
Ensuring safe landing in low visibility conditions
Standardizing pilot decision-making
Reducing human error during critical flight phases
Missing the decision height callout without proper visual reference can lead to serious safety risks.
Visual References Required at Decision Height
At DH, pilots must see at least one of the following:
Approach light system
Runway threshold
Runway edge lights
Touchdown zone markings
Runway centerline lights
If none are visible, a go-around is mandatory.
How Decision Height Is Determined
Decision height depends on:
Type of approach (ILS CAT I, II, III)
Airport infrastructure
Aircraft certification
Pilot qualification
Weather minima
Lower DH requires higher levels of automation and redundancy.
Decision Height Callouts in the Cockpit
Modern aircraft use radio altimeters to provide automatic callouts such as:
“Minimums”
“Decision Height”
These alerts ensure pilots do not miss the critical decision point during approach.
Conclusion
Decision Height is a cornerstone of safe instrument flying. It ensures pilots make timely, standardized decisions during precision approaches, especially in poor visibility conditions. By strictly adhering to decision height procedures, aviation professionals maintain safety, consistency, and regulatory compliance.
Whether you are a pilot in training or an aviation professional, mastering the concept of decision height is essential for confident and safe IFR operations.
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